Two variations of an EOR (enhanced oil recovery) technique have been presented at a Society of Petroleum Engineers (SPE) Asia pacific conference.

The miscible enhanced oil recovery (EOR) technique, presented by PL McQuire, and BM Holt, is proving to be effective in field tests at Prudhoe Bay in Alaska. Two distinct variations of this technique have been evaluated.
Vertical variation
The vertical Miscible Injectant Stimulation Treatment (MIST) process involves completing a production well at the bottom of a thick, continuous, watered-out interval. A large slug of miscible injectant (MI) is injected, followed by a small slug of chase water. The MI sweeps rock not contacted by previous MI injection and drives EOR oil to offset producers.
Lateral variation
In the lateral MIST process, a horizontal lateral is drilled along the base of the reservoir from either a production well or an injection well. MI is injected sequentially into several intervals along the lateral to mobilise EOR oil from previously unswept areas. The lateral well is then returned to normal production or injection service.
Simulation data indicated that the vertical MIST process could recover more than 200,000 barrels of incremental oil per well at initial rates of up to 1,000 bpd. Calculations for the lateral MIST process indicated potential recovery of more than 1 million bbl of incremental EOR per lateral.
Field results of the MIST process have been mixed but are encouraging overall. Incremental EOR response from the first MIST lateral well was approximately 1,400,000 barrels, resulting in a technical and economic success.
Response from three subsequent MIST lateral injectors varied widely. The first vertical well MIST showed little response, but it did provide valuable insight into the performance of the process at Prudhoe Bay. The subsequent vertical well MIST, which had a much larger volume of injected MI, was very successful and eventually recovered over 1,100,000 barrels. Cumulative incremental EOR from the MIST wells through one month was more than 5,000,000 barrels, with average incremental oil-production rates of approximately 4,000 barrels per day (bpd). Based on these successful results, an ongoing program of additional MIST wells is planned.
The Prudhoe Bay field, located on the north coast of Alaska, is the largest oil field in North America, with total estimated reserves of roughly 13 billion barrels and a current production rate of approximately 600,000 bpd.
The field is overlaid by a large gas cap, and the majority of the field is being produced by gravity drainage. Waterflood and miscible EOR operations at Prudhoe Bay, which are confined to the downstructure and peripheral areas of the field, are producing roughly 200,000 bpd.